A number of apparatuses for treating multifilament yarn with air jets were known in the past, some providing cocurrent movement of air blasts and yarn. In many of the apparatuses, the air entering is introduced into a chamber or bore at an angle to the travel of yarn in a path that intersects the axis of the bore and this air jet results in fluttering or oscillation of the yarn. In others, the air introduction into the chamber or bore is tangential so that the air column whirls around the chamber or bore and imparts twist to the yarn.
A typical example of the first class is represented by the patent to London, U.S. Pat. No. 3,824,776. In this patent one or more multifilament yarns are pretexturized and then passed through a bore of an air jet apparatus in a straight path which follows the axis of the bore. Air at relatively high pressure is introduced into the bore at an angle of 45.degree. - 75.degree. with the air flow in the bore being cocurrent with the yarn direction. The patent describes only the use of pretexturized yarn and produces non-uniform, intermittent entanglement with nodal points between portions which are fluffed out. The non-uniform entanglement apparently somewhat resembles tiny sausage links or beads.
Another patent belonging to the same group is the Palm U.S. Pat. No. 2,942,402, June 28, 1960. One of the critical features of the invention is that there is a significant amount of leakage of air back through the yarn guide even though this is filled to a considerable extent by yarn. In Palm the yarn is fed to the bore with substantial overfeed and moves through the bore along a path which follows the axis of the bore. The product produced by Palm is voluminous and contains loops of individual filaments which project from the main body of the yarn.
The second class of air jet apparatuses, in which air is introduced tangentially, includes my earlier U.S. Pat. Nos. 3,653,196, Apr. 4, 1972; 3,700,391, Oct. 24, 1972; and 3,831,363, Aug. 27, 1974. In each of my three patents the whirling air stream causes the yarn which is introduced to spin in the form of one or more loops similar in appearance to a jumping rope. This introduces a large amount of false twist and the false twist is allowed to untwist with an abrupt change in direction, which produces extremely effective texturization. Very substantial overfeed of the yarn going into the texturizing chamber is required.